Organic optoelectronic devices, including circuits, such as organic light emitting diodes, organic electrochromic displays, organic photovoltaic devices and organic thin film transistors, are known in the art and are becoming increasingly important from an economic standpoint.
As a specific example, organic light emitting devices (“OLEDs”), including both polymer and small-molecule OLEDs, are potential candidates for a great variety of virtual- and direct-view type displays, such as lap-top computers, televisions, digital watches, telephones, pagers, cellular telephones, calculators and the like. Unlike inorganic semiconductor light emitting devices, organic light emitting devices are generally simple and are relatively easy and inexpensive to fabricate. Also, OLEDs readily lend themselves to applications requiring a wide variety of colors and to applications that concern large-area devices.
In general, two-dimensional OLED arrays for imaging applications are known in the art and typically include an OLED display area that contains a plurality of active regions or pixels arranged in rows and columns. FIG. 1A is a simplified schematic representation (cross-sectional view) of an OLED structure of the prior art. The OLED structure shown includes a single active region 15 which includes an electrode region such as anode region 12, a light emitting region 14 over the anode region 12, and another electrode region such as cathode region 16 over the light emitting region 14. The active region 15 is disposed on a substrate 10. With the aid of a sealing region 25, the cover 20 and the substrate 10 cooperate to restrict transmission of oxygen and water vapor from an outer environment to the active pixel 15. Traditionally, light from the light emitting layer 14 was transmitted downward through the substrate 10. However, other OLED architectures are also known in the art, including “top-emitting” OLEDs and transparent OLEDs (or “TOLEDs”). Moreover, structures are also known in which the positions of the anode 12 and cathode 16 in FIG. 1A are switched as illustrated in FIG. 1B. Such devices are sometimes referred to as “inverted OLEDs”.
Unfortunately, certain OLED structure components, such as reactive metal cathode components, are susceptible to oxygen and moisture, which exist in the ambient atmosphere and can produce deleterious effects that can severely limit the lifetime of the devices. For example, moisture and oxygen are known to increase “dark spot areas” in connection with OLED structures. The organic materials utilized in a conventional OLED structure can also be adversely affected by environmental species such as water and oxygen. Components of various other organic optoelectronic devices such as organic electrochromic displays, organic photovoltaic devices and organic thin film transistors are likewise susceptible to attack from exterior environmental species including water and oxygen.
One approach to mitigating the adverse affect of moisture and oxygen is to attach a cover to the substrate, for example, with the aid of sealing region 25 as shown in FIGS. 1A and 1B. The attachment of the cover is typically done under a clean, dry, inert atmosphere, and employs adhesives such as epoxy resins that can be deleterious to the OLED device. Moreover, epoxy resins suitable for sealing a cover to an OLED substrate are generally not flexible. Therefore, the use of epoxy resins is undesirable particularly where a flexible OLED (FOLED) is desired. These additional processing steps are time consuming and complex, decreasing the production efficiency and increasing the expense associated with manufacturing OLEDS.
It has also been proposed, for example, in U.S. Pat. Nos. 6,146,225 and 6,268,695, both of which are incorporated herein in their entireties, to form a multi-layer coating (also referred to herein as a composite barrier layer) directly onto an OLED device by use of a polymer multilayer process (or “PML” process). The PML process is disclosed, for example, in U.S. Pat. Nos. 4,842,893, 4,954,371, and 5,260,095 and 6,224,948, all of which are incorporated herein in their entireties. The PML process is advantageous because it is a vacuum compatible process which produces a conformal coating that does not require the separate attachment of a preformed multi-layer cover, as discussed above. Moreover, the PML process produces a composite barrier layer with good resistance to moisture and oxygen penetration.
However, when used to directly deposit a composite barrier layer on an OLED device, the PML process itself can cause damage to the active region of the OLED. For example, the PML process commonly involves the use of acrylic monomers that are polymerized in situ on a substrate by ultraviolet radiation and heat. It is believed that when the PML process is employed to form a multi-layer protective layer on an OLED, diffusion or seepage of the acrylic monomer into the layers in the active region of the OLED, i.e., the cathode layer, light emitting layer(s) and anode layer, causes damage thereto. Moreover, the heat employed during the PML process may also cause damage to one or more of the layers in the active region of the OLED. Damage to the OLED is manifested in, for example, reduced opto-electronic performance characteristics such as brightness, operating voltage, and light emission efficiency as is known in the art.